The differential diagnosis between sporadic adenoma and colitis-associated neoplasia is difficult. Clinical, histological and molecular genetic methods are available to recognise a difference between these two entities. The aim of the present analysis was to check known criteria in a large series of patients and 352 patients with ulcerative colitis and concomitant intraepithelial neoplastic lesions [149 adenomas (A), 123 colitis-associated intraepithelial neoplasias (N), 80 carcinomas (K)] were investigated. Clinical history helped to identify patients with sporadic adenoma since patients with colitis-associated neoplastic lesions presented with different data such as age (A: 61.3+/-13 years, N: 48.4+/-16.4 years, K: 53.9+/-16.9 years), duration of disease (A: 6.9+/-8.1 years, N: 11.9+/-10 years, K: 13.6+/-9.6 years), frequency of pancolitis (A: 28.6%, N: 56.3%, K: 48.3%) and frequency of solitary lesions (A: 83.7%, N: 23.1%, K: 51.9%). The differential diagnosis between adenoma and colitis-associated neoplasia in patients with ulcerative colitis appears to be possible but the diagnosis should only be made in the remission phase. Furthermore the patients need a careful endoscopic and bioptic follow-up. If in doubt one should consider colitis-associated neoplasia especially when there are multiple intraepithelial neoplastic lesions. Long-term follow-up studies are urgently needed.